FLAMEK8sBakend

A FLAME Backend for Kubernetes. Manages pods as runners in the cluster the app is running in.

The current implementation is very basic and more like a proof of concept. More configuration options (resources, etc.) will follow.

Installation

def deps do
  [
    {:flame_k8s_backend, "~> 0.3.0"}
  ]
end

Usage

Configure the flame backend in our configuration or application setup:

  # application.ex
  children = [
    {FLAME.Pool,
      name: MyApp.SamplePool,
      backend: FLAMEK8sBackend,
      min: 0,
      max: 10,
      max_concurrency: 5,
      idle_shutdown_after: 30_000,
      log: :debug}
  ]

Prerequisites

Env Variables

In order for the runners to be able to join the cluster, you need to configure a few environment variables on your pod/deployment:

The POD_NAME and POD_NAMESPACE are used by the backend to get informations from your pod and use them for the runner pods (e.g. env variables).

apiVersion: apps/v1
kind: Deployment
spec:
  selector:
    matchLabels:
      app: myapp
  template:
    spec:
      containers:
        - env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.namespace

RBAC

Your application needs run as a service account with permissions to manage pods:

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: myapp
  namespace: app-namespace
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: app-namespace
  name: pod-mgr
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["create", "get", "list", "delete", "patch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: myapp-pod-mgr
  namespace: app-namespace
subjects:
  - kind: ServiceAccount
    name: myapp
    namespace: app-namespace
roleRef:
  kind: Role
  name: pod-mgr
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      serviceAccountName: my-app

Clustering

Your application needs to be able to form a cluster with your runners. Define POD_IP, RELEASE_DISTRIBUTION and RELEASE_NODE environment variables on your pods as follows:

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
        - env:
            - name: POD_IP
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: status.podIP
            - name: RELEASE_DISTRIBUTION
              value: name
            - name: RELEASE_NODE
              value: my_app@$(POD_IP)